The present invention relates to a weft insertion system and method for a fluid jet loom which can provide optimum weft inserting performances in accordance with an instantaneous condition of a weft yarn.
Japanese Patent Provisional Publication No. 60-162837 shows a weft insertion method in which a weft tension is detected during weft insertion, and a weft inserting condition such as a pressure or timing of a fluid jet is controlled in accordance with a difference between the sensed weft tension and a predetermined standard.
In this method, the weft yarn condition is detected during the weft insertion period. Therefore, the corresponding corrective action is not possible until the next weaving cycle because of limitations in the response speed of a pressure regulator and valve. In this sense, this control method is a feedback control. In such a feedback control however, it is difficult or impossible to make uniform the timing of the termination of the weft insertion especially in the case of spun yarn (cotton yarn) whose properties are not even along the yarn length. This tends to create mispick and deterioration of woven fabric quality. The unevenness of the spun yarn affects the timing of termination of the weft insertion by affecting the pulling force applied on the yarn by the fluid jet stream, and hence the initial acceleration of the weft yarn.
Japanese Patent Provisional Publication No. 60-162838 shows another weft insertion method, which is designed to measure a flying velocity of a weft yarn by sensing a change of an amount of a stored weft yarn during weft insertion, and to control a weft inserting condition such as the fluid jet pressure, in accordance with the result of the measurement. However, this method is also unsatisfactory in that the corrective action cannot be effected within the same weaving cycle. This is true especially in recent high speed looms. When the operating speed of a loom is as high as 800 rpm, for example, the speed of weft insertion must be about 25 m/s. At such a high speed, this conventional method is not appropriate to control the weft inserting condition before the weft insertion. When the air pressure in an air jet loom is changed between a low pressure and a high pressure by switching over from a high pressure air tank to a low pressure air tank, a residual high pressure air considerably retards the actual change of the air pressure. In such a case, this method is unable to immediately make a proper air pressure wave form.